markh1 1 Posted May 12, 2015 I've noticed my revs seem low compared to my indicated road speed. At 3000 I have an indicated 60mph in 4th gear (and around 3500 at 70). I'm running what I believe to be a standard, albeit rebuilt 1600GT engine with a standard 4 speed, 3.89/3.9 rear axle and 185/70x13s. I'm sure this is wrong - tried this speed-rpm-calculator which suggests I should be around 500 revs higher...anyone have any experience of what could be wrong here? I dont think speedo is far out as running past speed cameras in 50mph zone suggests I am running at 50mph compared to other road users (unless of course they are only doing 45!). cheers. Quote Share this post Link to post Share on other sites
the-ford-cortina.com 226 Posted May 12, 2015 running past speed cameras in 50mph zone suggests I am running at 50mph compared to other road users (unless of course they are only doing 45!). cheers. THEY WILL BE , MODERN CAR SPEEDOS SHOW about 10% higher than reality - check your actual speed against speedo with a sat nav on a straight road Mind you this problem you have doesnt look to be a problem to me , are you sure you dont have a 3.77 diff ? some Es were fitted with 3.77s WHEN NEW IT WAS AN OPTION :thumbup: Quote Share this post Link to post Share on other sites
markbagelboy 0 Posted May 12, 2015 Inside the back of tacko you have a calibration dial which you can Adjust via the instrument light holder. Which you have to remove With a small screw driver adjust dial .you can use a Strobe light with a tacko reader would help To confirm correct revs Mark Quote Share this post Link to post Share on other sites
markh1 1 Posted May 12, 2015 Thanks for responses. 1 - My axle: Pretty sure I have a 3.89 or 3.9 - build plate says 'J' which I believe means as much - do you know what a 3.77 is indicated by? 2 - Rev counter needs adjustment: If I do have a 3.89/3.9 then this could be the answer - will try to get an accurate rev counter hooked up - the car certainly seems reluctant to rev beyond 4500 so that might be the answer (although how many people actually try to push it beyond that on a standard engine I'm not sure). Quote Share this post Link to post Share on other sites
rubberhead 4 Posted May 12, 2015 Thanks for responses. 1 - My axle: Pretty sure I have a 3.89 or 3.9 - build plate says 'J' which I believe means as much - do you know what a 3.77 is indicated by? 2 - Rev counter needs adjustment: If I do have a 3.89/3.9 then this could be the answer - will try to get an accurate rev counter hooked up - the car certainly seems reluctant to rev beyond 4500 so that might be the answer (although how many people actually try to push it beyond that on a standard engine I'm not sure). hi mate,i have the opposite problem to you ,at 60mph im at about 5000 rpm.yes you can adjust the rev counter setting but only on a series2,on series 1rev counter there is no adjustment screw hole,your running same tyres/axle /engine as me and ive been playing with mine trying to sort out problem,ran a test on it with a separate tacho /meter and found my rev counter reading 1150rpm at tickover but really its at 850rpm.what I need to know is at say 4000rpm is it still reading 300rpm higher or is it graduated so the higher it revs the bigger the error Quote Share this post Link to post Share on other sites
markh1 1 Posted May 13, 2015 hi mate,i have the opposite problem to you ,at 60mph im at about 5000 rpm.yes you can adjust the rev counter setting but only on a series2,on series 1rev counter there is no adjustment screw hole,your running same tyres/axle /engine as me and ive been playing with mine trying to sort out problem,ran a test on it with a separate tacho /meter and found my rev counter reading 1150rpm at tickover but really its at 850rpm.what I need to know is at say 4000rpm is it still reading 300rpm higher or is it graduated so the higher it revs the bigger the error Yeah good point - not sure how far the discrpancy changes with increase in revs - I'd assume it is exponential and increases more as revs goes up... May try adjusting the rev counter although wary I may make things worse - as has been known to occur :( Quote Share this post Link to post Share on other sites
petermac 5 Posted May 17, 2015 Checked mine today on run out and it indicated 3000rpm @ 60mph so it seems correct to me. :thumbup: Peter. Quote Share this post Link to post Share on other sites
rubberhead 4 Posted May 18, 2015 cheers pete,that gives me a benchmark to calibrate from. Quote Share this post Link to post Share on other sites
markh1 1 Posted May 18, 2015 got my build plate in a muddle - it says 'A' not 'J' so pretty sure thats a 3.89 or 3.9 - looks like I am in similar position to everyone else :thumbup: Mark Quote Share this post Link to post Share on other sites
